rhag ofn - in case, lest
Conjunctions are linking words e.g. and , but , because , or. They are used to connect clauses or sentences to form more complex sentences. e.g. 'I want to go out tomorrow but it is going to rain all day.' Many Welsh conjunctions take a particular construction ( ' i' or ' bod' ) to link them with what follows in the sentence.
Rhag ofn can appear with either the 'i' or 'bod' constructions.
see: How do conjunctions work in Welsh? for more details.