fejben

Fejben is a Hungarian adverb meaning "in the head" or "in one’s head." It refers to mental actions performed without external aids or tools, such as thinking, calculating, or planning, done internally rather than aloud or on paper.

Etymology and form: Fejben is derived from the noun fej (head) with the locative suffix -ben, giving "in the head." Hungarian locatives use -ban/-ben depending on vowel harmony; fej ends with a front vowel, so the correct form is fejben.

Usage: Fejben is used with verbs that express internal cognitive activity. Common collocations include fejben tartani (to keep in mind), fejben számolni (to do mental arithmetic), and fejben eldönteni (to decide mentally). It can function as an adverbial modifier or be part of idiomatic expressions. Examples: A választ fejben számoltam ki. (I calculated the answer in my head.) Fejben tartom a tervet. (I keep the plan in my head.) Fejben eldöntöttem, mit tegyek. (I decided in my head what to do.)

Notes: Fejben is widely used in everyday speech and informal writing to denote cognitive processing without external aids. In more formal contexts, speakers may opt for paraphrases such as "mentálisan" (mentally) or restructure the sentence to avoid a heavy reliance on the adverb, depending on style and register.