Coming out, as an animal in a crest

• Having only the forepart visible, as a beast in heraldry
• Emerging, in heraldry
• Having only the forepart visible, in heraldry
• Having only the upper part showing, as a heraldic beast

Wiktionary Word definitions in Wiktionary
a. 1 (context obsolete English) issuing, emerging 2 (context heraldry of an animal English) Having only the upper half depicted

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Issuant \Is"su*ant\ ([i^]sh"[-u]*ant), a. (Her.) Issuing or coming up; -- a term used to express a charge or bearing rising or coming out of another.