The prefix kâld- can only be combined with the words broer brother and suster sister, resulting in the words kâldbroer half-brother and kâldsuster half-sister. Hence, this prefix is clearly unproductive. One can use these words to refer to a brother or a sister who either has a different father or mother than oneself.

This prefix must have been grammaticalized from the adjective kâld cold, which may also have the metaphorical meaning 'unrelated' or 'remotely related' (particularly within families; see Veen (1984-2011 s.v. kâld, 9)). It must therefore be considered to be a prefixoid. Alternative prefixes with the same function are heal-, kalf- and pot-. While heal- is the commonly used prefix, kâld-, kalf- and pot- can be considered as being obsolete.

The prefix is pronounced as [kɔ:t]. In derivations it bears the stress, e.g. KÂLDsuster half-sister.