Plan popular number with Delta (6)
I believe the answer is:
intend
'plan' is the definition.
(I know that plan is a more specific form of intend)
'popular number with delta' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'number' becomes 'ten' (ten is a kind of number).
'with' means one lot of letters go next to another.
'delta' becomes 'd' (phonetic alphabet: alpha, bravo, charlie etc.).
'in'+'ten'+'d'='INTEND'
(Other definitions for intend that I've seen before include "Purport" , "Have as purpose or in mind" , "Tinned (anag.)" , "Mean - purpose" , "Mean; aim" .)