Antahkarana is a term used by the Vedantins to include mind, Buddhi, Chitta and Ahankara.
When used in a broad sense, it means the internal instrument.
Antah means internal; Karana means instrument.
It is the inner instrument (as distinguished from the term Bahya Karana, outer instrument or the senses or Indriyas) through which you sense, perceive, think and reason out.
Ahankara is derived from Prithvi-Tanmatra.
(Tanmatras are Sukshma Bhutas or subtle elements. The five gross elements are derived from the Tanmatras.)
Chitta is derived from Jala-Tanmatra; Buddhi from Agni-Tanmatra; mind from Vayu-Tanmatra; heart from Akasa-Tanmatra.
Mind is Chetana (intelligent) when compared with the senses.
It is Jada (non-intelligent) when compared with Buddhi.
Sankhya Buddhi or Buddhi in Sankhya Philosophy is will and intellect combined.
Some put Chitta under mind, Ahankara under Buddhi.
To be continued ...