Caesar Cipher in Python 3
Line spacing is important for readability. leave two spaces before your functions and don't have so many after. be sure to also be consistent about whitespace around operators.
word.lower() does not change the case of word but rather returns a string that is the lowercase equivalent of word.
The following can be simplified using the modulo operator

charvalue = ord(i) +key
if ( charvalue &gt; 122):
    charvalue = ord('a') + (charvalue -123)
    encryptedstring += chr(charvalue)

else:
    encryptedstring += chr(charvalue)


becomes

charvalue = ((ord(i) - ord('a')) + key) % 26 + ord('a')

Your cipherencrypt() function does not currently support negative keys (see #2), but if it did, cipherdecrypt() could be written as:

def cipherdecrypt(word, key):
    return cipherencrypt(word, -key)

In python it is recomendend to do this kind of replacement with a comprehesnion:

def cipherencrypt(word, key):
    return "".join(
        chr(((ord(i) - ord('a')) + key) % 26 + ord('a'))
        for i in word.lower()
    )

Your cipher does not currently support space or any non latin character. If passed a non latin character, like space, your program will not be able to decrypt it. consider expanding your range to all printable characters or adding a special case for space.