सङ्कल्पान्मन इत्याहुर्बुद्धिरर्थस्य निश्चयात् ।अभिमानादहङ्कारश्चित्तमर्थस्य चिन्तनात् ॥ ३४५ ॥
In plain words
Because it wills and imagines, they call it mind. Because it settles what an object is, intellect. Because it claims everything as 'I' and 'mine', ego. Because it keeps turning an object over in thought, citta.
Close to the Sanskrit
From willing, 'mind' — thus they say; 'intellect', from the ascertainment of an object; from self-appropriation, 'ego'; 'citta', from the thinking-over of an object.