With “Am up”, use delaying tactics. Say “Don’t feel well” (8)
I believe the answer is:
malinger
'use delaying tactics say don't feel well' is the definition.
I can't judge whether this defines the answer.
'with am up' is the wordplay.
'with' is a charade indicator (letters next to each other).
'am' becomes 'ma' ('MA' can be a synonym of 'am').
'up' becomes 'linger' (I can't justify this - if you can you should give a lot more credence to this answer).
'ma'+'linger' is 'MALINGER'.
Can you help me to learn more?
(Other definitions for malinger that I've seen before include "skive off school, maybe" , "Slack in germinal fashion" , "Feign illness to avoid work" , "Pretend to be ill to avoid work" , "To shirk work" .)