Left open is a phrase used to define an item or situation that is not closed or secured properly. There are various synonyms available to describe this state of being, and some examples include "unlocked," "unsealed," "unfastened," "ajar," "unclosed," "unprotected," "unguarded," and "exposed." Each word has a unique flavor that may be more appropriate for specific contexts. For example, "unguarded" may be more suitable for descriptions of vulnerable areas of a building, while "unfinished" may be more appropriate for projects or assignments that require further completion. Ultimately, choosing the right synonym for "left open" depends on the context and the intended meaning.