Interrogate

This is one of the 117 mis-spellings listed as 'Common difficulties' in the section on 'Spelling' within 'Writing' in UEfAP.

The verb interrogate, and related words such as interrogation, interrogating interrogative and interrogator have one doubled consonant, the '-r-'. All the other letters are single.

Etymological note: interrogate and its relatives are derived from the Latin interrogare, formed from the prefix inter-, either as a preposition 'between [people]', or an adverb 'at intervals', together with the verb rogare 'to ask'. So the combined forms such as interrogation have one '-r-' from inter- and one from rogare, which constructs the double '-rr-' of the Englsih spelling.