Rudra (means)=Lord sri Siva
Aksha(means)= means eyes
Rudraaksham means Lord sri.Siva's eyes
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Another way of looking at it is :-
"A"karaathi "Ksha"kaaraantham is "AKSHA"( in Sanskrit first letter is "A" and last letter is "Ksha" -as we say in English "A" to "Z") So Aksha means all things created in the Universe starting with the letter "A" and ending with the letter Ksha( A to Z) in the whole Universe is Lord SIVA-
Rudra + Aksham=Rudraaksham
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A third way fo looking at it is :-
Ksharam(means)=Destructable
Aksharam (means)=Non-destuctable-eternal
Rudra(Lord Siva is Non-destructable,-Eternal-(Nithyam)because He is Para Brahmam-So Rudra is Akshram)
Acharya Sri Sankara puts this idea in "Soundarya Lahiri" in a beautiful verse (all sri Sankara Acharya's verses are beautiful) starting with "Sudhamapi Aasvaadya------Na Sambhoho Dava Janani Thaadanga mahima) -Somayaji