Semi-visibilities can be synonymously referred to as hazy, unclear, or somewhat visible. Other terms that can be used include indistinct, vague, misty, or obscure. Semi-transparency, partially visible, or indeterminate are also good synonyms.
These words are useful when describing situations where an object or image is not totally visible, or where the level of visibility is gradual. For example, a semi-visible character in a film may be obscured by a fog or shadow, while a semi-visible item on a dark kitchen counter may be difficult to identify.
Whatever the context, there are always synonyms available to help imbue your writing with imagery and clarity.