security blanket

noun

1. a blanket or other familiar item carried especially by a young child to provide reassurance and a feeling of psychological security.
2. someone or something that gives a person a sense of protection or a feeling of security: His wealthy uncle is his security blanket.

noun

1. a policy of temporary secrecy by police or those in charge of security, in order to protect a person, place, etc, threatened with danger, from further risk
2. a baby’s blanket, soft toy, etc, to which a baby or young child becomes very attached, using it as a comforter
3. informal anything used or thought of as providing reassurance

Something that dispels anxiety, as in I always carry my appointments calendar; it’s my security blanket. This colloquial term, dating from about 1960, was at first (and still is) used for the blanket or toy or other object held by a young child to reduce anxiety.