kulcsra
Kulcsra is a term used in Hungarian linguistics and everyday language as part of the phrasal verb construction kulcsra zárni, meaning to lock up or to lock with a key. The form combines the noun kulcs (key) with the postposition -ra and functions as a means or instrument in the expression. The overall meaning is securing something by locking it using a key.
In usage, kulcsra zárni appears with a direct object that is being locked. For example, szobát kulcsra
Variants and nuance: some speakers also use kulccsal or other instrumental expressions to emphasize the means
See also: Hungarian phrasal verbs, zárni, kulcs, grammatical instruments in Hungarian.