1a Go under the knife (Damocles was under a sword)
7d Intending - 'i' (one) + 'N(ew) T(estament) ending'
15a Dappling - 'din' (containing) 'appl(e; mostly)' + 'g(ood)'
18a Berberis - 'ber(i)beri' (spares 'i'; one) + 's(mall)'
21a Scorpion - 'pi (irrational) o (love)' (in) 'scorn'