Letter from abroad for volunteer soldiers until recently (5)
I believe the answer is:
theta
'letter from abroad' is the definition.
(letter of the Greek alphabet)
'volunteer soldiers until recently' is the wordplay.
I cannot really see how this works, but
'volunteer' could be 'ta' (member of the Territorial Army, volunteer regiment) and 'ta' is found in the answer.
The remaining letters 'the' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'for' is the link.
Can you help me to learn more?
(Other definitions for theta that I've seen before include "Make amends for" , "letter from Athens" , "Character from overseas" , "classic character?" , "Foreign character" .)