Synonyms for Prolonged:

adj.

•continued (adjective)
interminable, persevering, unceasing, sustained, extended, continued, protracted, maintained, persistent, abiding.
•drawn-out (adjective)
continued, lengthened, sustained, extended, protracted.
•durable (adjective)
lifetime, long, everlasting, incessant, perennial, lengthy, long-life, livelong, enduring, durable, eternal, interminable, lifelong, lasting, perpetual.
•extended (adjective)
drawn-out, dull, lengthy.
•long (adjective)
drawn-out, protracted, long-drawn-out.

n.

constant, never-ending, for some time, long-term, on and on. continue, continuing, lingering. excite, long-drawn-out, Overlong, dragging. •prolonged (noun)
drawn-out, long, lengthy, chronic, protracted, lengthened, extended, elongated.

v.

•continued (verb)
extended, Persisted, Persevered, continued, abided, sustained, protracted, maintained.
•endured (verb)
Endured, Outlived, outlasted, Lasted, Perpetuated.
•extended (verb)
elongated, expanded, stretched, enlarged, lengthened.
•lengthened (verb)
elongated, extended, stretched, expanded, lengthened.

Other synonyms:

never-ending, long-drawn-out, Overlong, lingering. constant, dragging, long-term. continuing. •Other relevant words:
continue, continuing, drawn-out, long-drawn-out, lingering, dull, Overlong, never-ending, dragging, chronic.

Usage examples for prolonged

1. On the east the land was prolonged out of sight. – An Antarctic Mystery by Jules Verne

2. Jim Cal had crawled out of bed after a somewhat prolonged conversation with Wade. – Judith of the Cumberlands by Alice MacGowan

3. There followed a prolonged silence. – The Bars of Iron by Ethel May Dell