By oneself in plant pinching indefinite number (5)
I believe the answer is:
alone
'by oneself' is the definition.
(I've seen this before)
'plant pinching indefinite number' is the wordplay.
'plant' becomes 'aloe' (aloe is a kind of plant**).
'pinching' means one lot of letters goes inside another (taking inside).
'indefinite number' becomes 'n' (I've seen this in other clues).
'aloe' placed around 'n' is 'ALONE'.
'in' is the link.
(Other definitions for alone that I've seen before include "Exclusively, by oneself" , "without another" , "Isolated from others" , "Solo" , "Without anybody or anything else" .)