Enigmatic Variations 1765 The Seventh Note by Chalicea

So three clues lack a definition but are local names for two unclued entries. Alternate clues have an extra letter in the wordplay which give an instruction. As preambles go pretty straight forward.

Once all clues were solved the extra letters spell out SHADE ITS NAME FOUR LETTERS. So what is it? The unclued entries yield THE ABONIMABLE SNOWMAN with the penny droppy from the middle row SNOWMAN.

As to the undefined entries they are the three types of the abonimable snowman with YETI to be shaded in the middle column bottom 4 cells

• RANG SHIM BOMBO A smaller type of yeti. It stands 3 to 5 feet tall, has reddish-grey fur, and lives in forested mountain valleys below the snow line. Some locals consider them harmless or juvenile yetis
• CHUTI The classic, ape-like yeti. It stands about 5 to 8 feet tall, has reddish-brown or brown hair, a conical head, and walks on two or four legs. Many researchers note this type closely resembles or stems from sightings of the Himalayan brown bear.
• NYALMO (Nyalmo (or Nilamo): The largest and fiercest type. It stands roughly 13 to 20 feet tall, features black fur, and lives at high altitudes above 13,000 feet.)

The title the (ye) and seventh note (ti) indicating the subject matter – or that is my take anyway.

Thanks Chalicea both educational and fun – and nothing on the diagonal!

Key * anagram; underline definition; Rev. reversed; DD double definition; Unclued entries; Undefined entries

Across
1 & 25 Across See preamble (3 words)
THE ABONIMABLE

9 Ridges of rock and rubble principally including sulphur (4)
aa (rock) + r (rubble principally) around S (sulphur) = ASAR

S 11 Priest, crafty in a scholarly manner in the past (7)
clerk (priest) + sly (crafty) = CLERKLY

13 Intimate high-quality dining service (5)
DD CHINA

H 14 Retrograde about onset of tyranny, chose short sword (5)
Rev. chose around t (onset of tyranny) = ESTOC

15 Linesman caught up in desperate opposition (4)
Rev. hidden desperaTE OPposition = POET

A 16 Uncooperative ports returned money given for service (7)
Rev. ports + pay (money given for service) = STROPPY

17 About soft not originally selected fine-grained rock (6)
a(about) + p (soft) + elite (selected) – e = APLITE

D 18 Announces dramatically shed lard (7)
(shed lard)* = HERALDS

20 Palm tree with medicinal properties lopped (3)
vital (with medicinal properties) – vl (lopped) = ITA

E 22 Late official essentially reversed summons to appear (5)
Rev late + ic (official essentially) = CITAL

23 One night in Marseille for person from the north (5)
I(one) + nuit (night in Marseille) = INUIT

25 See 1 Across
SNOWMAN

I 28 Hoard of Roman javelins in untidy hollow (5)
plia (Roman javelins) in uy (untidy hollow) = UPLAY

29 Aged fellow could not oddly peg out (5)
cOuLd (oddly) + die (peg out) = OLDIE

T 32 Dashed over a while back (3)
DD tore (dashed) = ORE

33 Historical tenure of military station on outskirts of glebe (7)
thana (military station) + ge (outskirts of glebe) = THANAGE

S 35 Male descendant to compete with, shown publicly (6,2 words)
son (male descendant) + vie (to compete with) = w (with) = ON VIEW

38 Company spread out in practice of dressing as fictional character (7)
co (company) + splay (spread out) = COSPLAY

N 40 One of original Finnish stock alights near bears going west (4)
Rev. hidden aligHTS NEar = ESTH

41 Amateur boxing live; support in form of letter (5)
ham (amateur) around be (live) = H-BEAM

A 42 India’s rich soil in some subarea gardens (5)
Hidden subaREA GARdens = REGAR

43 Nautical fitting inside is not terminated (7)
Hidden iS NOT TERminated = SNOTTER

M 44 Swindles reflected in bygone conveyances (4)
Rev scams (swindles) = SACS

45 Brahmin mobs go wild (13, 3 words)
(brahmin mobs go)* = RANG SHIM BOMBO

Down
E 1 Burrowing creatures turning up a section of earth’s crust (5)
Rev. a plate (section of earth’s crust) = TALPA

2 Carefully move top of loose supporting framework (5)
ease (carefully move) + l (top of loose) = EASEL

F 3 Regularly using fabrics, fit pieces for Trump’s waterproof overshoes (7)
fAbRiCs FiT pIeCeS =  ARCTICS

4 Lifted chunk of most evil old mock-pearl (6)
Rev. hidden mosT EVIL Old = OLIVET

O 5 Angry; bigoted intermittently about strike-breaker (5)
bIgOtEd around rat(strike-breaker) = IRATE

6 Endlessly false and wrong at heart too (4)
als (endlessly false) + o (wrong at heart) = ALSO

U 7 Drug: deceptively I coloured it up (12,2 words)
(I coloured it up)* = LOOP DIURETIC

8 Surrounds foreign body in dubious NY sects (7)
(NY sects)* = ENCYSTS

R 10 Basic photo pro sadly reveals fear of being observed (12)
(basic photo pro)* = SCOPTOPHOBIA

11 Wooden shelter in outskirts of Cagliari (5)
hut(wooden shelter) in ci (outskirts of Cagliari) = CHUTI

L 12 Regularly keep originally rare old gold coin for type of shrub (6)
KeEp + r (originally rare) + rial (old gold coin) = KERRIA

16 In Glamis display measure of yarn for Irish fisherwoman maybe (7)
shaw (In Glamis display) + ley (measure of yarn) = SHAWLEY

E 19 Upset ordinary contest in board game (4)
Rev. o (ordinary) + duel (contest) = LUDO

21 Animal manages climbs, gripping tree (4)
Hidden animAL MAnages = AMLA

T 24 Place type of stone in salmon trap (7)
put (place) + chert (type of stone) = PUTCHER

26 My loan reorganised (6)
(my loan)* = NYALMO

T 27 Long ago to a great extent old-style Republican event upheld (7,2 words)
Rev. os (old-style) + r(Republican) + event = NEVER SO

30 Astutely evade mobile funfair vehicle (6)
dodge(astutely evade) + m(mobile) = DODGEM

E 31 Metal alloy in rocky ravine (5)
(ravine)* = INVAR

34 Country garden right in heart of Philistine city (5)
r(right) in Gath (Philistine city) = GARTH

R 36 Small island realm from time to time for followers of religion (5)
isl (small island) + ReAlM = ISLAM

37 Any person lost who’s old (5)
who’s + o(old) = WHOSO

S 39 Once clasp painful emotion (4)
spang (once clasp) = PANG