Give one's word the Spanish articulation (5)
I believe the answer is:
vowel
'articulation' is the definition.
(thesaurus)
'give one's word the spanish' is the wordplay.
'give one's word' becomes 'vow' (I've seen this in another clue).
'the spanish' becomes 'el' ('the' in Spanish).
'vow'+'el'='VOWEL'
(Other definitions for vowel that I've seen before include "Type of letter such as A" , "Letter representing sound" , "A, E, I, O or U" , "Kind of letter of the alphabet" , "Letter such as i or u" .)