Almost lost spot for ball (5)
I believe the answer is:
gonad
'ball' is the definition.
(synonyms)
'almost lost spot for' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'lost' becomes 'gone' (similar in meaning).
'spot for' becomes 'ad' (I am not sure about this - if you are sure you should believe this answer much more).
'gone' with its last letter taken off is 'gon'.
'gon'+'ad'='GONAD'
Can you help me to learn more?
(Other definitions for gonad that I've seen before include "one 19A [CASTRATO] 's missing" , "organ" , "Private part" .)