1. ARCHAIC - CHAI[r] in ARC.
5. GRAMPUS - SUP reversed on GRAM. Nagoya's football club used to have eight of these cetaceans.
9. SCURVIEST - S A CURVIEST.
10. VISTA - ST in VIA.
11. RICER - R + ICER. Not heard of this N. Am. word defined by Oxford as 'A utensil with small holes through which boiled potatoes or other soft food can be pushed to form particles of a similar size to grains of rice.'
12. FUSILLADE - US + ILL in FADE. 'Deviation in the air' describes my golf shots admirably, and sounds so much better than slice, which is what we hackers call our 'fade'.
14. PLAIN CHOCOLATE - INCH O' COLA in PLATE.
17. ACHILLES TENDON - so biffable, I thought it was an angram of A VERY COLD DEATH. But, as John points out below, it's actually A, CHILLEST (very cold), END (death), ON (possible). My mum ruptured each of hers, both times playing tennis.
21. STOP WATCH - STOP WATCH. Come on then, how many of you bunged in 'slow coach'? TOP in SWATCH.
23. PLANK - PLAN[c]K. Heard of this 'un.
24. IGLOO - [b]IG + LOO.
25. FRIGIDITY - F + RIGIDITY. If I was given to such pronouncements, I would say there was a whiff of sexism about this. As it is, I love it.
26. TUMBLER - a whimsical clue with very modest pretensions.
27. TIE-DYED- - [pictur]E in TIDY + ED.
1. ASSERT - sounds like 'a cert'.
2. COUNCIL - UNC[o] in COIL. Unco can mean strange as well as very.
3. ADVERBIAL - VARIABLE + D*.
4. COEFFICIENT - CO + EFFICIENTLY. Would that all scientific clues were clued so generously!
5. GET - TEG reversed.
6. ANVIL - hidden. I got a 'treble treble' with ANVILLED in Scrabble yesterday, so watch out for the verb.
7. PASSATA - S + A in PASTA. A tomato paste I've never heard of.
8. SEA FEVER - EA + F in SEVER for the Masefield encomium to life on the ocean wave.
13. SHORT-SHRIFT - R in SHORT SHIFT. We had this phrase the other day.
15. OENOPHILE - PI[g]EONHOLE*.
16. DAY SHIFT - well, if you cross the date line you change day.
18. HOODLUM - LOUD* in HOM[e].
19. OPACITY - A + Y in OP CIT.
20. OKAYED - KAY in OED. Kay pops up in Malory's Morte Darthur, most notably in Book 4 with Gawain, Arthur and Gryfflet to defeat those pesky northern kings.
22. WHORL - WHO + R + L. My last in, even though I now use a fingerprint to access my iPad. Well, when it works.
25. FAR - FAR[e]. Last by name and very possibly last by nature...