Hand carved in an aventurine cabochon.
"hold fast" is an old sailors command- grab a line or secure rigging firmly so they would not be washed overboard during a storm.

Stay strong, show perseverance, and keep to your values, even when the going gets hard.
framed in 14 K with a nice big bale, with an interior diameter of about 6 x 4 mm, this pendant is about an inch and 3/4 high with the bail.