Which verbiage would you use to describe this party?

Question

An engagement cocktail party of 15-18 people. People would be asked to dress nice. (no tie)
But
no Jeans
On the invite should I call it a soiree or a gala?

Answer 1

The English way would be to specify on the invitation exactly what it was.

'(Name).cordially invites ...(Name of guest) ..for
Cocktails to celebrate the engagement of ...(names)
at..(address) on (date) followed by time.of event.
Dress.(Smart casual)
R.S.V.P.

By doing this you are paying your guest the courtesy of informing them exactly what you are providing and by telling them that it is a cocktail party you are inferring that there is a time limit on the event.
Cocktails or drinks is taken to mean pre-dinner drinks and your guests should depart no later than 8 p.m.
If you wish to extend that because you are to provide food or a buffet then specify Cocktails and Buffet.
Soiree and gala would not be used to describe this.We would call such an event a 'Reception'
Smart casual tells them jeans are a 'no' but that suits are not required.
R.S.V.P. followed by your contact number or name/address will let you know in advance the numbers you can expect to attend.

Answer 2

Soiree. Gala sounds more like a large formal event.

Answer 3

gala sounds too formal and big
soiree looks funny printed but between the two I'd go with soiree.

Answer 4

You don't give the party a name. You just mention what's going on (cocktails), the dress code, and possibly what's being celebrated (the engagement). (I say "possibly" because you might prefer to make the engagement announcement a surprise.)

Answer 5

soirre