7 Cask, pin. C, second (letter) to 'act' and Ask, seek.
17 Drop the 'e' in cares.
14 Vole, Vol(unteer) and E(ast). It's a term used in playing cards, to win every trick in one deal.
21 The answer is only eight letters, it's a thematic entry. The phrase 'Run the ...' is quite common. A five-letter word for 'barren' and the usual three-letter tennis term,
..... the grid yesterday, with the thematic solutions, and most of the extra letters identified, but not enougjvto find the 6 letter word. I will have another go! LOL
if you google the first 3 or 4 words generated by the extras...
2,7,6,5... the required 6 letter word comes up...i think it's a latin word for the thematic word ....it's vertically shown in the SW of the grid...