mess

1 mess /ˈmɛs/ noun
plural messes
1 mess
/ˈmɛs/
noun
plural messes
Britannica Dictionary definition of MESS
1 
a  [count] : a very dirty or untidy state or condition — usually singular
b  [singular] : something or someone that looks very dirty or untidy
2 
[count]
a  : a situation that is very complicated or difficult to deal with
b  : something that is not organized well or working correctly
3 
[singular] informal
a  : someone who is very unhappy, confused, etc.
b  US : someone who is showing a lot of emotion especially by crying
4 
[count] : the place where people in the military eat
— called also mess hall
5 
[singular] US, informal : a large amount of something — + of
6 
informal : solid waste from an animal
[count]
[noncount]

make a mess of

: to ruin (something) or to make many mistakes in doing (something)
2 mess /ˈmɛs/ verb
messes; messed; messing
2 mess
/ˈmɛs/
verb
messes; messed; messing
Britannica Dictionary definition of MESS

mess around

[phrasal verb] informal or British mess about
1 
: to spend time doing things that are not useful or serious : to waste time
2 
: to have sex with someone who is not your husband, wife, or regular partner
— often + with
3 
mess (someone) around/about British : to cause problems or trouble for (someone) especially by making changes that are not expected
4 
mess around/about with (something)
a  : to use or do (something) in a way that is not very serious
b  : to handle or play with (something) in a careless or foolish way

mess up

[phrasal verb] informal
1 
: to make a mistake : to do something incorrectly
— often + on
2 
mess (something) up or mess up (something)
a  : to make mistakes when you are doing or making (something)
b  : to make (something) dirty or untidy : to make a mess of (something)
c  : to damage or ruin (something)
: to damage or change (something) so that it does not work properly
3 
mess (someone) up or mess up (someone)
a  US : to beat and injure (someone)
b  : to make (someone) very upset and unhappy

mess with

[phrasal verb] informal
1 
mess with (someone) : to cause trouble for (someone) : to deal with (someone) in a way that may cause anger or violence
2 
mess with (something)
a  chiefly US : to deal with or be involved with (something that causes or that could cause trouble)
b  : to handle or play with (something) in a careless way : to mess around with (something)
3 
◊ In very informal English, something that messes with your mind/head causes you to feel confused.