Matriarch held beheaded monarch (5)
I believe the answer is:
elder
'matriarch' is the definition.
(thesaurus)
'held beheaded monarch' is the wordplay.
'beheaded' means to remove the first letter (the head of the word is removed).
'monarch' becomes 'er' (abbreviation for Elizabeth Regina).
'held' with its first letter removed is 'eld'.
'eld'+'er'='ELDER'
(Other definitions for elder that I've seen before include "Woody shrub - used for wine, tea or cordial" , "more mature" , "Senior - church official" , "Older or two" , "Senior member - plant" .)