What Aikido means
The word Aikido is actually a composition of three Japanese words : Ai , Ki and Do Those three words are written using the Japanese Kanji alphabet which is primarily used to express philosophical concepts originating from the chinese culture.
The literal meaning of Ai is "union" or "matching". Metaphorically it is used as "harmony", "unity", "balance". An interesting fact is that the word Ai, using another ideogram, means "love". This ideogram meaning "love" appears multiple times in the Aikido Founder's Morihei Ueshiba texts.
Ki (Chi in Chinese) is the probably the most difficult part of the word as it is one of the basic elements of the far east cultures. The closest rendition in English is "spirit", but it is frequently used by the Japanese as part of more composite words that are used in their everyday life (eg. Η κοντινότερη απόδοσή του στα ελληνικά είναι το "πνεύμα", όμως οι ιάπωνες χρησιμοποιούν τη λέξη αυτή ως συνθετικό για πολλές καθημερινές τους λέξεις (cheerful bad tempered, healthy, sick etc). In the Aikido context the closest rendition of the word Ki is "energy", the life force that exists within every person and in nature.
Do (Tao in Chinese) is also one of the basic parts of the Japanese culture. It can be translated metaphorically as "way", "path" ,"course" or "journey". Japanese add Do to their words as an ending to various activities, giving them a feeling of a road to personal fulfillment and perfection. Many martial arts use Do, especially in the 20th century and thereafter when the samurai era came to an end and people turned to more peaceful quests.
In conclusion, the words Ai Ki Do can be translated as "the way of uniting with the energy","the way of harmonization" or the "way of harmony". Actually any translation is acceptable as long as it takes into account the Aikido's founder fundamental message : The goal is always to achieve the perfection of the person, something that can only be achieved through constant training.