achievement _noun 

ADJECTIVES

extraordinary, outstanding, remarkable, notable
・His research in the field of medicine was recognized as an outstanding achievement.

great, major, tremendous, monumental • considerable
・Winning the race was a great achievement for him.

important, significant, noteworthy, crucial • impressive
・Overcoming his fear of public speaking was a significant achievement.

fine, no mean
・Completing the marathon in under three hours is no mean achievement for a novice runner.

crowning, main, proud, supreme
・Her artwork's recognition in the gallery was a proud achievement.

real, true • meaningful • proud
・Saving enough money to buy a house was a real achievement for them.

unique, unprecedented, rare
・Discovering a new species of plant in the wild was a rare achievement for the biologist.

concrete, solid • modest
・Increasing sales by 50% in just six months was a concrete achievement for the sales team.

lasting, long-standing, lifelong, memorable
・Overcoming personal challenges and growing stronger is a lasting achievement.

personal • collective
・Climbing the mountain was a personal achievement he had dreamed of.

architectural, artistic, cultural, economic, educational, engineering, literary, scientific, sporting, technical, technological 
・Developing a new software program was a technical achievement for the company.

VERBS

be
・Getting an A on the test was a significant achievement for Sarah. 

constitute, represent 
・For many students, graduating from college constitutes a significant achievement.

honor • celebrate
・The team gathered to celebrate their outstanding achievement of winning the championship.

PREPOSITIONS

in 
・Her achievement in academics earned her a scholarship to a prestigious university.

PHRASES

quite an achievement
・Managing to finish the project ahead of schedule was quite an achievement for the team.

a feeling/sense of achievement
・Completing the puzzle gave her a great sense of achievement.

a lack of achievement
・His persistent procrastination resulted in a noticeable lack of achievement.

a level/standard of achievement
・The team's ability to meet every milestone demonstrated a high level of achievement.