ACROSS
 7. <way to indicate name> MONOGRAM = (MAN + GROOM)*
 8. IS LAMB - B = ISLAM <non-Christian belief>
10. <energy> PIZZAZZ = ZZ after PIZZA
11. <constable> OFFICER = OFF + ICER
12. O_ C_ U_ L_ + I_ = OCULI <windows>
13. (TEN SATINS)* = NATTINESS <dapper quality>
15. EP I THETA - A = EPITHET <descriptive term>
17. <leftovers> RESIDUE = (I REUSED)*
19. (SATANIST'S)* = ASSISTANT <henchperson?>
22. ABLE* outside G = BAGEL <there's a hole in one>
23. <displeasure> CHAGRIN = CHA + GRIN
25. <daisy> CHICORY = CHICO _R_ _Y_
26. <dismisses> SACKS = "SAX"
27. E VENT OED = EVEN-TOED <description of some ungulates>

DOWN
 1. <Greek music-player> BOUZOUKI = B_ OUZO + UK I
 2. L HISTOGRAM* = LOGARITHMS <mathematical functions>
 3. <shameless> BRAZEN = BRA + ZEN
 4. I'M POST OR = IMPOSTOR <fake>
 5. <minor argument> TIFF = ←F FIT←
 6. CLOC[-k] HE = CLOCHE <hat>
 9. <British writer> MARY SHELLEY = (ALLEY RHYMES)*
10. (.n)PROVEN ANCES(t.) = PROVENANCES <origins>
14. <drunkenness> INSOBRIETY = (NOISY BRIT)* otuside E
16. <some toy vehicles> TRAIN SET = ←ART← + INSET
18. <hero> DO-GOODER = DOG (O inside ODER)
20. <stiffen> STARCH = ST ARCH
21. <changed course> TACKED = "TACT"
24. _R _A _S _P = RASP <file>