be
keep sth
We keep everything professional at work.

remain
He tried very hard to remain professional.

purely, strictly
He insisted that his relationship with the duchess was purely professional.

be, look, seem, sound
Their designs look very professional.

extremely, fairly, very, etc.
highly, truly
He dealt with the problem in a highly professional way.

thoroughly, totally
increasingly
almost

be
become, go, turn

fully
He wants to turn fully professional.

Professional is used with these nouns:
accountability, accountant, actor, actress, advice, adviser, archaeologist, army, artist, aspiration, assassin, assistance, association, athlete, athletics, autonomy, background, ball, baseball, basketball, biologist, body, bowling, boxing, burglar, capacity, career, circuit, class, cleaner, coach, code, colleague, commitment, competence, conduct, connection, cook, counselling, counsellor, courtesy, credentials, credibility, cricket, criminal, culture, dancer, degree, designer, detachment, development, diploma, diplomat, discipline, discretion, distance, distinction, duty, economist, education, elite, environment, ethics, etiquette, exam, excellence, experience, expert, expertise, fee, fight, finish, football, footballer, fulfilment, gambler, golf, golfer, guidance, guide, help, historian, hockey, identity, incompetence, independence, institute, instruction, integrity, interest, jealousy, job, journal, journalism, journalist, judgement, killer, kitchen, knowledge, league, librarian, life, link, literature, look, man, manager, manner, meeting, military, misconduct, musician, name, negligence, negotiator, obligation, obscurity, occupation, opinion, orchestra, organization, outfit, painter, partnership, peer, people, performance, performer, personnel, philosopher, photographer, photography, pilot, player, politician, practice, pride, production, psychologist, psychology, qualification, rank, reason, recognition, recording, referee, register, regulation, relationship, reputation, responsibility, rivalry, rugby, salon, scientist, service, singer, skill, snooker, soccer, society, soldier, specialist, specialization, sport, sportsman, sportswoman, staff, standard, standing, status, success, tennis, theatre, thief, touch, tournament, trader, trainer, training, translator, trustee, woman, work, worker, workshop, writer, writing