Same, together 

동일 = sameness, oneness
동료 = co-worker, colleague
동감(하다) = agree, sympathise (feel the same, same feeling)
동의(하다) = concur, agree
동갑 = same age
동의어 = a synonym
동시 = the same time
공동 = cooperation, collaboration, union
동기 = people who enter a school/company/army in the same year
동창 = graduates in the same year
동성 = same sex
합동 = combination, union
협동(하다) = cooperate

Movement

활동 = activity, action
운동 = exercise
자동 = automatic
동물 = animal
행동 = action, behaviour
동작 = movement
동사 = verb
진동 = vibration
감동 = moved/touched (emotionally)
변동 = change, fluctuation 
이동(하다) = movement
자동차 = car

Winter

동절기, 동계 = the winter season
동계올림픽 = the winter olympics
동면 = hibernation
동복 = winter uniform
냉동 = freeze
냉동실 = freezer
동지 = the winter solstice

East 

동쪽 = east (direction)
동해 = the east sea
동남아시아 = southeast asia
중동 = the middle east
동양 = the east
동양인 = asian 
동대문 = the east gate of seoul

Valley, village

인사동 = Insadong
동사무소 =  village office
동장 = the chief of a village office
동네 =one’s neighborhood, a village
동굴 = cave

Child 

동화 = fairy tale, children’s book
동시 = nursery rhymes
동심 = the mind/heart of a child, the innocence of a child
악동 = bad child, mischievous child
아동 = child
아동복 = children´s clothing
아동 학대 = child abuse
아동 보호 = child protection