A word of thanks with article and letter (5)
I believe the answer is:
theta
'letter' is the definition.
(theta is a kind of letter)
'a word of thanks with article' is the wordplay.
'a word of thanks' becomes 'ta'.
'with' is a charade indicator (letters next to each other).
'article' becomes 'the' (the 'definite article' part of speech).
'ta' after 'the' is 'THETA'.
'and' acts as a link.
(Other definitions for theta that I've seen before include "Make amends for" , "character in Marathon" , "Greek character" , "classic character?" , "letter from Argos?" .)