import re
text = """"
\nword1 meanings
\nword123 measings
\nword12345 meanings
"""
maxLen = len(max(re.findall(r"^\S+", text, re.M), key=len))
result = re.sub(r"(\S+)[^\S\r\n]+", lambda m: m.group(1) + ((maxLen + 1) - len(m.group(1))) * " ", text)
print(result)
aW1wb3J0IHJlCgp0ZXh0ID0gIiIiIgpcbndvcmQxICAgICBtZWFuaW5ncwpcbndvcmQxMjMgICAgICAgICBtZWFzaW5ncwpcbndvcmQxMjM0NSAgICAgICAgbWVhbmluZ3MKIiIiCgptYXhMZW4gPSBsZW4obWF4KHJlLmZpbmRhbGwociJeXFMrIiwgdGV4dCwgcmUuTSksIGtleT1sZW4pKQpyZXN1bHQgPSByZS5zdWIociIoXFMrKVteXFNcclxuXSsiLCBsYW1iZGEgbTogbS5ncm91cCgxKSArICgobWF4TGVuICsgMSkgLSBsZW4obS5ncm91cCgxKSkpICogIiAiLCB0ZXh0KQpwcmludChyZXN1bHQpCg==